Bearer technologies (e.g. GSM, UMTS) available in different territories can vary significantly. Thus, unlike many other countries with UMTS bearer technologies (3G), Japan does not have associated GSM (2G) networks. This is of considerable inconvenience for users of GSM handsets who wish to “roam” in Japan.
To receive a new call, a mobile terminal will need to be in registered in a paging area with the network. There are a number of problems that arise at the boundaries of paging areas in cellular networks of a particular bearer technology. In particular, customers may experience difficulties establishing new calls due to congestion in location registration signalling (idle state signalling) at cell boundaries—this scenario can arise when large numbers of terminals cross boundaries simultaneously, as would be the case for commuters on trains or in densely populated areas where cells cover smaller areas. Clearly, the route of a train can cross and re-cross cell boundaries many times leading, on occasions, to protracted denial of new calls.
Under GSM (and UMTS) standards, location registration signalling at cell boundaries is performed by storing a current Location Area (LA), or for UMTS Routing Area (RA), value—this value is associated with a particular cell and thus a respective base station (node B). In idle state, the terminal checks at cell change whether the new cell is still associated with the stored LA/RA—if there has been a change of value the terminal is forced to carry out a location/routing area update (LAU/RAU).
Denial of new call facility in one bearer technology need not prevent the use of a second bearer technology for which there is no signalling congestion. In at least some 2G/3G networks, combined 2G/3G MSCs and/or SGSNs, potentially with combined 2G/3G LAs and potentially with combined RAs are deployed. One reason for this is to limit the idle mode signalling caused by mobiles toggling between 2G and 3G coverage areas.
To address this problem in territories lacking an alternative bearer technology, a common UMTS plus GSM arrangement solution has been suggested which is based on a concept of “eXtended Areas”. In place of the storage of a single RA, the terminal is adapted to store a list of associated RAs—referred to hereinafter as XAs: and rather than comparing the detected RA to a single stored RA it is the detected XA is compared to all the members of the XA list. Only if the detected XA is not a match for any XA on the XA list will there be a routing area update.
Enhancements to the “area” concept of 3G without corresponding enhancements to 2G are liable to mean that operators face increased 3G-2G signalling load if they “enhance” their 3G area concept. This is undesirable.
It is highly desirable that there is a solution that works effectively on 2G (i.e. GSM), 3G (i.e. UMTS) and combined 2G/3G networks.
The GSMA have a work item specifically addressing such problems referred to as the “registration in densely populated areas” (RED) concept. It is further desirable that the RED concept is added to both 2G and 3G networks, and in both packet switched (PS) and circuit switched (CS) domains in a backward compatible manner.
This imposes some constraints on the solutions, and, in developing the concept, it is necessary to ensure that the solution can be retro-fitted onto the existing systems.
3G UMTS is probably more flexible in its capabilities than 2G GPRS which, in turn, is somewhat more flexible than 2G-Circuit Switched (i.e. GSM).
In each case, the XA concept cannot be introduced without altering the operation of the location registration process.